HomeMy WebLinkAboutRexburg WWTP FPS PowerPoint Presentation v4City of Rexburg WWTP
Facilities Planning Study
August 17, 2022
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WWTP Facility
Purpose:
Evaluate Existing Conditions
Estimate Future Needs
Propose Capital Improvements
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Planning Periods Requirements
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Influent Water Quality
Note: 2021 Data
* High strength domestic WW, Metcalf & Eddie fifth edition Table 3-16
•Rexburg’s average influent concentrations of biochemical oxygen demand (BOD5), chemical oxygen demand (COD), and total suspended solids (TSS) were significantly higher than what is
typically observed in high-strength domestic wastewater.
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Design Parameters
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Headworks
• The Headworks building consists of an Influent Parshall flume, Mechanical Step screens, and a grit removal chamber
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Headworks Deficiencies
Parshall Flume
Inaccurate Readings for Influent Flow
Mechanical Screens
Insufficient current Capacity
Grit Chamber
Insufficient Capacity for Planning Period
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Headworks Expansion
• Replace Parshall flume with new flowmeter or Parshall flume.
• Add 2 new Step Screens and keep current Mechanical Screens as redundant units.
• Install new Vortex grit chamber.
• Enlarge headworks building to fit new equipment
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Bio-Tower
• A Bio-Tower is part of the primary biological treatment processes. Wastewater is sprayed at the top of the Bio-Tower and flows through a trickling filter.
• The Bio-Tower was designed to remove 50% of the influent BOD or a maximum removal of 10,500 lbs/day and have a bacterial yield coefficient of Y=0.6. However, the facility has been
tested recently and the
structure was shown to remove
6,064 lbs/day of BOD with a yield
coefficient of Y=0.8.
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Oxidation Ditches
The oxidation ditches consist of Blowers, Basins and Mixers.
There are four existing oxidation ditches.
Blowers have recently been replaced
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Oxidation Ditches Deficiencies or Problems
High Solids Retention Time – Average 35 days
High Mixed Liquor Suspended Solids – Average 7000 mg/L
Food to Microbe Ration is low – 0.05 Average
No Redundancy
Insufficient Capacity for Future Demand
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Biological Treatment Recommendations
Address Downstream Processes
Construct 2nd Bio-Tower
Increased loading Capacity to treat BOD
Construct (2) Oxidation Ditches
Provide Redundancy
Provides Additional nutrient removal
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Secondary Clarification
A set of three clarifiers carries out secondary clarification where solids suspended in the liquid can settle to the bottom while water overtops a weir. The solids are then pumped towards
the RAS/WAS pump station.
RAS is returned to the Oxidation Ditches and returns to the Clarifiers.
WAS is sent to the Bio-Solids Treatment.
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Clarifiers
Clarifiers 1 and 2 have a 65’ diameter and have a design capacity of 1.72 MGD. Clarifier 3 has an 80’ diameter and a 2.59 MGD design capacity.
Design Loading Capacity 29 lbs/ft^2/day
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Clarifiers Deficiencies
No Redundancy
Any unit that is offline will cause the remaining Clarifiers to be overloaded.
Currently exceeding loading Capacity
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Clarifiers Recommendations
Address Downstream Processes
Add (2) 80’ Clarifiers
Add 1st Clarifier by 2024
Add 2nd Clarifier by 2027 or when the influent flow exceeds 4.2 MGD.
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U.V. Disinfection
• U.V. Disinfection is the last treatment process for the clarified water. The water flows around a series of Ultraviolet emitting lamps that render microorganisms inert or sterile.
The lamps are contained in modules and two modules make a bank. There are 4 banks; two are in operation and two are on stand-by. There is room to add more banks in the future.
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Bio-Solids Treatment
Bio-Solids Treatment includes the WAS and RAS Pump Station, a Solids Holding Tank, a Gravity Belt Thickener, a Thickened WAS Storage Tank, Pasteurization Tanks, an Anaerobic Digester,
Solids Dewatering, and Solids Storage.
Updated during current project
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Pasteurization Tanks
• The Rexburg facility has three Pasteurization tanks that each hold 2,650 gal of sludge currently at 3% concentration the design capacity states that each tank will hold 2,650 gal of
sludge at 6% concentration.
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Processing Bio-solids
The Pasteurization process is the unit that produce the Class A Bio-Solids for the Rexburg WWTP.
The Pasteurization Unit was part of the 2016 facility upgrade.
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Anaerobic Digester
The 2016 design states a VSS destruction of 62% or 6,021 lbs/day
According to statements from the operators, the digester does not provide a significant reduction in solids.
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Biosolids Deficiencies
Pasteurization Unit
Design Capacity
Processing 14,311 dry lbs/day
25,740 gallons per day
Current Conditions (2021)
Processing 13,252 dry lbs/day
Generation 16,970 dry lbs/day
Future Demand (2041)
Processing 29,504 dry lbs/day
Anaerobic Digester
30 Years old
Capacity
SRT of 20 days
No live Bacteria in the System
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Biosolids Recommendation
Increase Class A Capacity
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Proposed WWTP Facility
Upgrades
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Summary of facility upgrades
Headworks – Expansion
(1) Flowmeter
(2) Mechanical Screens
(1) Grit Chamber
Biological Processes
(1) Bio-Tower
(2) Oxidation Ditches
Clarification
(2) 80 ft Clarifiers
UV Disinfection
Channel depth modification
Bio-Solids
(1) Dryer
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Projected Schedule
2023 Design Class A Capacity Upgrades
2023 Design Headworks Upgrades
2023 Design Clarifier Upgrades
2024 Construction Class A Upgrades
2024 Construct Headworks Upgrades
2024 Construction of additional 80’ Clarifier
Design and Construction Oxidation Ditches and Bio-Tower when ADF exceeds 4.7 MGD
2027 Construction of additional 80’ Clarifier or when ADF exceeds 4.2 MGD
2032 UV Channel upgrades or when ADF exceeds 4.7 MGD
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Forsgren Associates, Inc.
208-356-9201• Forsgren.com
Dave Noel • dnoel@Forsgren.com
Kevin Harris • kharris@Forsgren.com
Jason Broome • jbroome@Forsgren.com
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